An Experimental Study Of The Characteristic Of Jet Flow Generated By Ship Propeller And Its Application

With the rapid development of the national economy,waterborne transportation has made appropriate progress.Dynamic conditions and maneuverability of ships have been greatly improved,but the velocity of wake flow generated increases accordingly.The wake flow of navigating ships has a more and more obvious effect on waters,which may affect the water environment.Previous studies are lack of deep investigation into such issues as whether the disturbance caused by navigation jet flow can result in bed bottom sediment incipient motion and re-suspension and further release the contaminants contained;therefore,further experimental demonstration and computational analysis is required.Therefore,an experiment of jet flow generated by ship propeller model was performed in a flume;in the experiment,the influence of flow velocity,water depth,propeller speed,parallel and counter flow directions on the propeller jet flow field was analyzed.Then,a comparative analysis was conducted on the research findings on the development rule of propeller jet flow;the results measured from real ships and the bed sediment survey data in the Changsha-Zhu Zhou-Xiangtan section of Xiang Jiang River,the conditions of sediment incipient motion and re-suspension was calculated.In this way,the influence of ship wake on bed surface sediment was evaluated.This work is of great guiding significance for harmonizing the relationship between river water environment protection and water transportation development.Here are the research findings:(1)It can be seen that the change in flow velocity,propeller speed,water depth and parallel and counter flow directions of ship may affect the propeller jet flow field.Concomitant water flow is generated during ship navigation,which is significantly different from the flow phenomenon generated by fixed propeller of the ship.(2)Analysis of the results of static and dynamic ship experiments in the flume shows that:compared with the condition in counter flow direction,the distance of jet flow development is longer in vertical direction when the ship direction is parallel to the water flow direction.When the ship direction is parallel to the water flow direction,with the increase of flow velocity,the distance of jet flow development in both axial and vertical directions reduces gradually;as the water depth increases,the distance of jet flow development in vertical direction decreases;with the increase of propeller speed,the distance of jet flow development in both axial and vertical directions increases.When the ship direction is counter to the water flow direction,as the flow velocity increases,the jet flow development trend in axial direction intensifies and that in vertical direction weakens;with the increase of water depth,the jet flow development trend in vertical direction weakens;as the propeller speed increases,the jet flow development trend in both axial and vertical direction intensifies.(3)Analysis of static and dynamic ship experiment results also shows the differences between the two ships:the time required for water surface recovery when the ship navigates in the direction parallel to the water flow direction is shorter than that when the ship navigates in the direction counter to the water flow direction.Under the same condition,the disturbance caused by propeller jet flow of the dynamic ship is weaker than that of the static ship;under the same condition,the distance of jet flow development of the static ship in vertical direction is longer than that of the dynamic ship.(4)Analysis of bed bottom sediment incipient motion and re-suspension under the effect of propeller jet flow shows that:when the ambient velocity is low,the initial velocity of propeller jet flow,bed water depth and sediment grain size are the main factors deciding whether the sediment moves or not.The higher the initial velocity of propeller jet flow is,the bigger the mean velocity on the jet flow cross-section will be;the mean velocity on the jet flow cross-section increases with the decrease of water depth.(5)The Changsha-Zhuzhou-Xiangtan section of Xiang Jiang River basically has developed into a reservoir featuring big water depth,very small ship navigation density,over 0.87mm mean grain size of bed sediment and little fine-grained sediment.Through computational analysis of the disturbance caused by propeller jet flow in dry season,it is found that the mean velocity on the jet flow cross-section is less than the sediment incipient velocity;the sediment suspension indicator is above 4 in most cases;bed sediment incipient motion and re-suspension is difficult in this section.Therefore,it can be judged that the influence on bed bottom sediment is insignificant during normal ship navigation in this reservoir area.